1. Field of the Invention
This invention in general relates to the field of ultrasound imaging, and more particularly concerns a system and method for ultrasound imaging of structures such as the spinal column and ribs, which reflect ultrasound at a variety of angles.
2. Description of the Prior Art
This invention arises out of a project to devise a device that would be useful in the diagnosis of scoliosis. Scoliosis is a disease resulting in the deformity of the spine. The disorder, which is a significant worldwide health problem, is characterized by both lateral curvature and rotation of the vertebrae. The cause of idiopathic scoliosis, which is the most common class of scoliosis, is unknown, but the symptoms generally appear during the developmental years. Failure to effectively treat the disorder in those cases where the curvature progressively grows worse leads to deformity of the torso and potentially, cardiopulmonary distress. Patients are often treated by orthopedic surgeons during the adolescent years of childhood by one or more methods which include external orthotic bracing, spinal fusion surgery, and electrical stimulation (internal and/or external) of the paraspinal muscles.
Presently, the most widely used clinical method employed to diagnose, assess, and track the course of the disease is standard x-ray imaging. Since there are no reliable methods yet available to predict the rate of progression of the disease, the patient is examined on a regular basis. Typically, a child will be subjected to a large number of x-rays over the course of the disease regardless of the treatment modality implemented. In many cases, no treatment is warrented, but the child is x-rayed periodically to verify that the curve has not progressed significantly. It therefore becomes highly desirable to develop a technique of detecting and monitoring scoliosis which will minimize or eliminate x-ray exposure. In recent years, great emphasis has been placed on the need to develop effective, safe methods of screening children in public schools.
Aside from the issue of safety, the x-ray instrumentation currently used does not lend itself optimally to the rapid assessment of scoliosis. For example, just the right contrast must be obtained and then the equipment must be run by a radiological specialist. Further, the orthopedic surgeon must ponder the x-ray and then perform certain geometric operations on the image in order to extract quantitative information regarding the nature of the spinal curvature. Another parameter which is becoming increasingly important to measure is the amount of vertebral rotation which accompanies the lateral curvature of the spine. This is presently difficult to accurately assess using x-ray.
Not many alternative means to x-ray for assessing scoliosis appear in the literature. One method currently under limited evaluation is called the Moire technique. This is an optical photographic technique which detects bilateral nonsymmetry in the surface features of the back. The method employs the principle of interference fringes. The patient's back is photographed through an interference screen or defraction grating. This results in a set of contour-line shadows on the photograph which is indicative of the surface topology of the back. The main shortcomings of this system are two-fold. First, there are no established scientific correlative studies relating visual surface features to spinal curvature. Secondly, the device is primarily aimed at screening rather than the quantitative assessment of the magnitude of the spinal curvature. Thus a system and method with which spinal curvature could be directly measured which can be repeatedly used without damage to a child or other person would be highly desireable.
As mentioned above, the system of the invention for overcoming the problems with the prior art methods of tracking scoliosis features ultrasound imaging. A wide variety of ultrasound imaging systems have been devised, although none of them known to us appear to be particularly suited for the imaging problem at hand. Examples of such imaging systems are disclosed in U.S. Pat. No. 4,242,912, which discloses a system including an array of transducers which are energized in cyclically selected groups, and U.S. Pat. No. 4,252,026, which discloses an ultrasound imaging system which employs a plurality of transducer elements for receiving echoes.